But where do they come from? How do these myths (and most of them turn out to be false) enter the conventional wisdom of health?

Some of the myths are true, but only for a small number of people.

"It's important to remember, in some of these myths, that it's different for a person who's been injured as opposed to someone who's healthy and not injured," Dr. Sherwin Ho, an orthopedic surgeon and director of the sports medicine fellowship at the University of Chicago Medical Center, told us when we spoke to him about exercise myths.

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"[For] those that are injured, some of these myths are actually true, and that's where they came from," he said.

While Ho said he would recommend some stretching for a patient with a history of injury, it might actually harm a healthy patient.

The best warm-up is not stretching, but a milder, slower version of the exercise you are about to do. Stretching afterward may help with flexibility, but stretching beforehand won't do anything to prevent injury.

And that isn't the only area where following what you may have heard without checking it out could harm you.

Though the Centers for Disease Control and Prevention tries to get many people vaccinated against influenza each year, many skip their shots out of fear that the vaccination will give them the flu.

But, as Dr. William Schaffner, chairman of the Vanderbilt Medical School Department of Preventive Medicine, notes, the vaccine doesn't contain a full flu virus.

"There's no way that the shot can give you a complete influenza virus that can then make you ill," he said.

In this case, he speculated, people may catch a cold around the time they are vaccinated and think the two are connected, but they are mistaken.

And that isn't the only mistake people make when it comes to attempts to ward off microscopic particles.

But washing your hands involves getting germs off the skin, not killing them. And the antibacterial ingredient in these soaps won't work fast enough when it is on the hands, but its effects haven't been fully studied in the environments it inhabits once it goes down the drain.

And antibacterial ingredients aren't the only treatment people turn to that doesn't prove its worth.

Many try local honey in an attempt to ward off allergic reactions to the plants that bloom around them each spring. But while honey may taste sweeter than antibacterial soap, it's not likely to give much relief.

The reason is that pollen from trees and grass tends to cause the irritation, while pollen from flowers is used to make honey.

"The pollen the honey is made out of is not the pollen that causes the allergies. It's not tree pollen and it's not grass pollen," said Dr. Douglas Leavengood, an allergist at Gulf Coast Asthma and Allergy in Biloxi, Miss. "As far as allergy goes, it's just the wrong type of pollen."

Of course, not every myth turns out to be a falsehood but that doesn't always mean the myth is harmless.

One of these is the idea of a "base tan," where people use tanning beds to get a tan before heading out to catch some rays, the idea being that they can avoid sunburn.

Well, the tanning bed will do the trick, but that doesn't eliminate the main complaint about tanning beds -- that they contribute to skin cancer.

"We're trying to just show that it's important for us to examine commonly held beliefs," said Dr. Aaron E. Carroll, director of the Center for Health Policy and Professionalism Research at the Indiana University School of Medicine, when explaining his article for the British Medical Journal back in December, which took a look at some common myths surrounding the holiday season.